Catalyst for preparing methanol through carbon dioxide hydrogenation as well as preparation method and application of catalyst

Abstract

The invention belongs to the field of catalysts for preparing methanol through carbon dioxide hydrogenation, and particularly relates to a catalyst for preparing methanol through carbon dioxide hydrogenation as well as a preparation method and application thereof. According to the catalyst, CuO and ZnO are used as active components and are uniformly dispersed on a hierarchical pore self-supporting nanosheet zeolite molecular sieve carrier to obtain a spherical catalyst; in the catalyst, CuO accounts for 8.3 to 34.7 percent by weight, and ZnO accounts for 3.6 to 15.2 percent by weight. The catalyst is used for catalyzing carbon dioxide hydrogenation to prepare methanol. According to the catalyst disclosed by the invention, due to the highly dispersed CuO / ZnO particles, the CO2 conversion frequency is relatively high, and the space-time yield and the unit generation rate of methanol are also relatively high; meanwhile, the catalyst is simple in preparation process and good in repeatability.

Description

Technical Field

[0001] The present invention belongs to the field of catalysts for hydrogenating carbon dioxide to methanol, and particularly relates to a catalyst for hydrogenating carbon dioxide to methanol, a preparation method thereof, and an application thereof. Background Art

[0002] CO2 emitted during human industrial production and life is a greenhouse gas that seriously threatens the earth's environment. Reducing anthropogenic CO2 emissions has become an urgent issue in the world today. Converting CO2 into valuable fuels or chemicals by catalytic hydrogenation of CO2 is a reliable means of reducing CO2 emissions. The industrialized process of hydrogenating CO2 to methanol is one of the most effective ways of hydrogenating and converting CO2. Methanol is a very important chemical raw material and also a non-petroleum-based clean synthetic fuel.

[0003] Most of the catalysts for hydrogenating CO2 to methanol are developed based on the catalysts for hydrogenating CO to methanol. The most studied catalysts are supported catalysts based on copper and zinc as the main components (Chem. Rev. 2020, 120, 7984 - 8034; Chem. Soc. Rev., 2020, 49, 1385 - 1413). The existing CuOZnOAl2O3 for industrial hydrogenation of CO2 to methanol still has the problem of limited space-time conversion rate and cannot achieve greater improvement. At present, improving the performance of catalysts by changing the catalyst composition and improving the catalyst preparation method is still an important research direction for each scientific researcher.

[0004] Chinese Patent CN1329938A relates to a preparation method of a methanol synthesis catalyst. The catalyst synthesized by this method is composed of CuO, ZnO, and Al2O3. The preparation process is as follows: the raw materials of the catalyst are prepared in two parts. One part is prepared by the co-precipitation method to obtain a co-precipitated substance containing copper, zinc, and aluminum compounds; the other part is prepared by the co-precipitation method to obtain a co-precipitated substance containing copper and zinc compounds; subsequently, the two co-precipitated substances are mixed, washed, dried, calcined, and formed.

[0005] Chinese Patent CN101444731A relates to a catalyst for hydrogenating CO2 to methanol. The catalyst is composed of the main active components Pd, Zn, and the promoter carbon nanotubes.

[0006] Chinese Patent CN101513615A relates to a preparation method of a catalyst for hydrogenating CO2 to methanol. The molar ratio of each component of the catalyst is Cu:Zn:Al:Zr:M = 45:45:10:5:2 (M is MnO, CeO2, Ag2O, Fe2O3, La2O3). The preparation method is as follows: 1) A mixed solution of aluminum nitrate solution and cobalt nitrate solution and a carbonate solution are co-precipitated in parallel flow to obtain a carrier precursor; 2) A mixed nitrate of copper, zinc and M and a carbonate solution are added in parallel flow to 1), and then aged, filtered, dried and calcined to obtain a methanol synthesis catalyst.

[0007] Chinese Patent CN111215084A relates to a preparation method of a copper-based catalyst for hydrogenating carbon dioxide to methanol, which mainly solves the problems of poor activity, especially poor stability of traditional copper-zinc-aluminum catalysts for hydrogenating carbon dioxide. The catalyst of the invention uses copper, zinc and aluminum as active components. By changing the preparation method of the catalyst, the zinc-aluminum components are first precipitated, aged and calcined at low temperature, and the reaction conditions are controlled to obtain a zinc-aluminum hydrotalcite precursor with higher stability and more favorable for copper dispersion. Then, the active component copper and the precursor are subjected to deposition precipitation reaction to finally obtain a new copper-zinc-aluminum catalyst suitable for hydrogenating carbon dioxide to methanol.

[0008] Chinese Patent CN101757943A relates to a preparation method of a catalyst for synthesizing methanol by hydrogenating CO2. Using HZSM-5 molecular sieve as the carrier and uranium and cobalt as the promoters, a Cu-Zn-Ce-Zr-HZSM-5 catalyst is prepared. The molar ratio of Cu / Zn is 2-4:1, the molar ratio of Ce / Zr is 1-3:1, the mass content of Cu-Zn is 30%-70%, and the mass content of HZSM-5 is 5%-50%.

[0009] At present, the reported catalysts for hydrogenating CO2 to methanol are mainly Cu-Zn series catalysts. The main carriers selected are Al2O3, TiO2, SiO2, etc. The preparation methods are mainly impregnation or co-precipitation. However, the main problems of the above catalysts are poor dispersion of active components, low conversion rate of CO2 per unit Cu, low methanol yield, and unsatisfactory catalyst performance. For industrial hydrogenation of CO2 to methanol, the research on these catalysts is not yet mature. Summary of the Invention

[0010] The purpose of the present invention is to solve the technical problems of low conversion rate of CO2, low space-time yield of methanol and poor dispersion of CuO in the current catalysts for hydrogenating CO2 to methanol, and to provide a catalyst for hydrogenating carbon dioxide to methanol, its preparation method and application.

[0011] To achieve the above purpose, the technical solution adopted by the present invention is

[0012] A catalyst for the hydrogenation of carbon dioxide to methanol, with CuO and ZnO as active components, is uniformly dispersed on a hierarchical pore self-supporting nanosheet zeolite molecular sieve support to obtain a spherical catalyst (with an average diameter of about 100 or 400 nm); among them, CuO in the catalyst accounts for 8.3 - 34.7 wt.%, and ZnO accounts for 3.6 - 15.2 wt.%.

[0013] The specific surface area of the catalyst is 90.0 - 433.3 m 2 / g, and the mesoporous specific surface area reaches 90.0 - 351.5 m 2 / g, and the mesoporous pore volume is 0.217 - 0.605 m 2 / g.

[0014] The active component particles with a size of 2 - 8 nm are uniformly dispersed and loaded on the surface of the catalyst support.

[0015] The support is two spherical hierarchical pore self-supporting nanosheet molecular sieve supports (SPP molecular sieves), the phase of the support is a five-membered ring chain zeolite molecular sieve, and their average sizes are 100 and 400 nm respectively. The specific surface area of the support is 581.1 - 630.2 m 2 / g.

[0016] A preparation method of the catalyst for the hydrogenation of carbon dioxide to methanol as described above,

[0017] S1 First, dissolve the Cu salt and Zn salt in water, and then add an organic dispersant to prepare a precursor solution;

[0018] S2 Immerse the support in the above precursor solution, and obtain the catalyst after drying and calcination; or, after calcination, immerse it repeatedly in the above precursor solution, and obtain the catalyst after drying and calcination.

[0019] The molar ratio of the Cu salt to the Zn salt is (6 - 8):3.

[0020] The solution concentration of the Cu salt in the mixed aqueous solution is 0.8 - 1.6 mol / L; and the solution concentration of the Zn salt is 0.3 - 0.8 mol / L.

[0021] Add an organic dispersant to the mixed salt solution to form a precursor solution of the metal salt.

[0022] The organic dispersant is one or more of ethylenediamine, citric acid, or polyvinylpyrrolidone.

[0023] The addition amount of the dispersant is 0.21 - 1.03 times the mass of the metal salt.

[0024] An application of the catalyst as described above in the catalytic hydrogenation of carbon dioxide to methanol.

[0025] The reaction of catalytic hydrogenation of carbon dioxide to methanol is carried out in a micro-pressure fixed-bed continuous flow reactor. The reaction temperature is 180 - 300 °C, GHSV = 3000 h -1 , V(H2):V(CO2) = 3:1, and the reaction pressure is 3 MPa; among them, the addition amount of the catalyst is 0.5 g.

[0026] The remarkable effects of the present invention compared with the prior art are as follows:

[0027] On the catalyst of the present invention, CuO / ZnO particles are highly dispersed. By adding an organic dispersant, they are uniformly dispersed in the mesopores and on the surface of SPP. Among them, ethylenediamine complexes with Cu to form Cu(en)2 2+ Ions are attracted into the mesopores of the carrier by electrostatic force and interact with the silanol groups on the nanosheets, thereby improving the dispersion degree of CuO / ZnO. At the same time, the particle size of CuO / ZnO is restricted by the mesopores of the molecular sieve carrier, thus greatly improving the conversion rate of CO2, the CO2 conversion frequency, the space-time yield of methanol, and the unit formation rate of methanol during the process of catalytic hydrogenation of carbon dioxide to methanol by the catalyst; at the same time, the preparation process of the catalyst is simple and has good repeatability. Description of the Drawings

[0028] Figure 1 The X-ray diffraction patterns of the carrier provided in the examples of the present invention and Examples 1 - 7: A, Carrier 1; B, Carrier 2; C, Example 1; D, Example 2; E, Example 3; F, Example 4; G, Example 5; H, Example 6; I, Example 7.

[0029] Figure 2 The N2 adsorption-desorption curves of the carrier provided in the examples of the present invention and Examples 1 - 7: A, Carrier 1 and Carrier 2; B: a, Example 1; b, Example 2; c, Example 3; d, Example 4; e, Example 5; f, Example 6; g, Example 7.

[0030] Figure 3 The scanning electron microscope images (SEM) of the carrier provided in the examples of the present invention and Examples 1 - 7: A, SPP-1; B, Example 1; C, Example 2; D, Example 3; E, Example 4; F, Example 5; G, SPP-2; H, Example 6; I, Example 7.

[0031] Figure 4Transmission electron microscope (TEM) images of the support provided by the embodiments of the present invention: A and B; transmission electron microscope (TEM) and scanning transmission electron microscope (STEM) images of Examples 1-7: B and F, Example 1; C and G, Example 2; D and H, Example 3; I and M, Example 4; J and N, Example 5; K and P, Example 6; L and Q, Example 7.

[0032] Figure 5 H2 temperature-programmed reduction curves of Examples 1-7 provided by the embodiments of the present invention: a, Example 1; b, Example 2; c, Example 3; d, Example 4; e, Example 5; f, Example 6; g, Example 7.

[0033] Figure 6 CO2 conversion rates and CO2 turnover frequencies of Examples 1-7 provided by the embodiments of the present invention: a, Example 1; b, Example 2; c, Example 3; d, Example 4; e, Example 5; e, Example 6; e, Example 7.

[0034] Figure 7 Methanol space-time yields (A) and methanol unit formation rates (B) of Examples 1-7 provided by the embodiments of the present invention: a, Example 1; b, Example 2; c, Example 3; d, Example 4; e, Example 5; f, Example 6; g, Example 7. Detailed implementation manners

[0035] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0036] The objective of the present invention is to provide a catalyst with a mesoporous self-supporting molecular sieve as the support, CuO and ZnO as the active components. By adding an organic dispersant to the precursor, the precursor can be better dispersed on the surface of the support or in the mesoporous channels of the support. Through the interaction between the precursor and the silanol groups on the surface of the support, the dispersion of the precursor is stabilized and improved, thereby increasing the dispersion degree of CuO and reducing the nano-size of CuO. Among them, when ethylenediamine is used as the dispersant, the Cu(en)2 2+ complex interacts with the silanol groups on the surface of the support nanosheets, which is more conducive to the dispersion of the precursor. A catalyst with highly dispersed CuO nanoparticles is obtained, and at the same time, the methanol selectivity and yield in the CO2 hydrogenation reaction are improved.

[0037] The supports used in the following exemplary embodiments were synthesized based on the methods in the literature (Science, 336 (2012) 1684-1687).

[0038] Support 1: First, tetraethyl orthosilicate was added to the template agent solution (25% aqueous solution). After stirring overnight, the sol was loaded into a hydrothermal reaction kettle (the initial gel ratio was 1SiO2:0.3TBPOH:11H2O:4EtOH). The crystallization reaction was carried out at 115 °C. The crystallization time was changed to 48 h, and it was placed in a rotary oven during crystallization (the rotation speed was 15 rpm). Subsequently, the solid obtained by crystallization was separated by centrifugation and washed 3 times with deionized water. The rotation speed during centrifugation was 25000 rpm, and the time was 30 min. The water in the sample was removed by freeze-drying. Finally, the powder was calcined in a muffle furnace. During calcination, it was heated to 550 °C at a rate of 2 °C / min and calcined for 12 h. Finally, Support 1 was obtained.

[0039] Support 2: Fumed silica was added to the template agent solution (25% aqueous solution) and stirred evenly. The sol was added to a hydrothermal reaction kettle (the initial gel ratio was 1SiO2:0.3TBPOH:11H2O:4EtOH). The crystallization reaction was carried out at 115 °C for 96 h. It was placed in a rotary oven during crystallization (the rotation speed was 15 rpm). Subsequently, the solid obtained by crystallization was separated by centrifugation and washed 3 times with deionized water. The rotation speed during centrifugation was 15000 rpm, and the time was 10 min. The water in the sample was removed by freeze-drying. Finally, the powder was calcined in a muffle furnace. During calcination, it was heated to 550 °C at a rate of 2 °C / min and calcined for 12 h. Finally, Support 2 was obtained.

[0040] The experimental methods used in the following examples are all conventional methods unless otherwise specified. The materials, reagents, methods, and instruments used, unless otherwise specified, are all conventional materials, reagents, methods, and instruments in this field, and those skilled in the art can obtain them through commercial channels.

[0041] The terms "comprising", "including", "having", "containing", or any other variation thereof used in the following examples are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or device containing the listed elements is not necessarily limited to those elements, but may include other elements not explicitly listed or elements inherent to such composition, step, method, article, or device.

[0042] When an equivalent, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper preferred values and lower preferred values, this should be understood to specifically disclose all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed individually. For example, when the range "1 to 5" is disclosed, the described range should be interpreted as including the ranges "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5", etc. When a numerical range is described herein, unless otherwise stated, the range is intended to include its end values and all integers and fractions within the range. In the specification and claims of this application, range limitations can be combined and / or interchanged, and if not otherwise stated, these ranges include all sub-ranges contained therein.

[0043] The indefinite articles "a" and "an" before the elements or components of the present invention do not limit the quantity requirements (i.e., the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the singular form of the element or component also includes the plural form, unless the quantity clearly refers only to the singular form.

[0044] Example 1: The preparation method of the catalyst for hydrogenating carbon dioxide to prepare methanol in this example is carried out according to the following steps:

[0045] S1: Add 9.64 g of Cu(NO3)2·3H2O and 5.94 g of Zn(NO3)2·6H2O (where Cu / Zn = 6 / 3) to 20 mL of deionized water, place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min, set the temperature at 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt, with the Cu ion concentration being approximately 1.6 mol / L and the Zn ion concentration being approximately 0.8 mol / L; add 16.4 g of citric acid as a dispersant to the mixed solution to prepare a precursor solution;

[0046] S2: Immerse 3 g of SPP molecular sieve (support 1) in 5 mL of the above solution, then dry it overnight in an oven at 100 °C, and then increase the temperature to 500 °C at a heating rate of 2 °C / min and maintain it at 500 °C for 4 h.

[0047] S3: Immerse the powder prepared in S2 in 4.5 mL of the above solution and repeat step S2 once to obtain the catalyst.

[0048] Example 2: The preparation method of the catalyst for hydrogenating carbon dioxide to prepare methanol in this example is carried out according to the following steps:

[0049] 1: Add 9.64 g of Cu(NO3)2·3H2O and 4.5 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 27 mL of deionized water. Place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min. Set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt. The Cu ion concentration is 1.28 mol / L, and the Zn ion concentration is 0.48 mol / L. Add 3 g of polyvinylpyrrolidone to the mixed solution as a dispersant to prepare a precursor solution.

[0050] S2: Immerse 3 g of SPP molecular sieve (support 1) in 5 ml of the precursor solution for 24 h. Then dry it overnight in an oven at 90 °C, and then heat it at a heating rate of 2 °C / min to 450 °C and hold it at 450 °C for 4 h.

[0051] S3: Add the powder obtained in S2 to 4.5 mL of the precursor solution and repeat the steps of S2 once to obtain the catalyst.

[0052] Example 3: The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol in this example is carried out according to the following steps:

[0053] 1: Add 9.64 g of Cu(NO3)2·3H2O and 5.10 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 40 mL of deionized water. Place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min. Set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt. The Cu ion concentration is approximately 0.8 mol / L, and the Zn ion concentration is approximately 0.34 mol / L. Add 14 g of ethylenediamine to the mixed solution as a dispersant to prepare a precursor solution.

[0054] S2: Immerse 3 g of SPP molecular sieve (support 1) in 5 ml of the precursor solution, then dry it overnight in an oven at 110 °C, and then heat it at a heating rate of 1 °C / min to 400 °C and hold it at 400 °C for 4 h. Obtain the catalyst.

[0055] Example 4: The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol in this example is carried out according to the following steps:

[0056] 1: Add 9.64 g of Cu(NO3)2·3H2O and 5.10 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 40 mL of deionized water. Place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min. Set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt. The Cu ion concentration is approximately 0.8 mol / L, and the Zn ion concentration is approximately 0.34 mol / L. Add 14 g of ethylenediamine to the mixed solution as a dispersant to prepare a precursor solution.

[0057] S2: Immerse 3 g of SPP molecular sieve (support 1) in 5 ml of the precursor solution, then dry it overnight in an oven at 110 °C, and then increase the temperature to 400 °C at a heating rate of 1 °C / min and hold it at 400 °C for 4 h.

[0058] S3 Repeat the operation of step S2 on the powder obtained in S2 three times to obtain the catalyst. The volume of the precursor solution for each impregnation is 4.5 mL; 4.5 mL; 4.5 mL.

[0059] Example 5: The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol in this example is carried out according to the following steps:

[0060] 1: Add 9.64 g of Cu(NO3)2·3H2O and 5.10 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 40 mL of deionized water, place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min, set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt, with the Cu ion concentration being approximately 0.8 mol / L and the Zn ion concentration being approximately 0.34 mol / L; add 14.0 g of ethylenediamine as a dispersant to the mixed solution to prepare a precursor solution;

[0061] S2: Immerse 3 g of SPP molecular sieve (support 1) in 5 ml of the precursor solution, then dry it overnight in an oven at 110 °C, and then increase the temperature to 400 °C at a heating rate of 1 °C / min and hold it at 400 °C for 4 h.

[0062] S3 Repeat the operation of step S2 on the powder obtained in S2 six times to obtain the catalyst. The volume of the precursor solution for each impregnation is 4.5 mL; 4.5 mL; 4.5 mL; 3.5 mL; 3.5 mL; 3 mL.

[0063] Example 6: The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol in this example is carried out according to the following steps:

[0064] 1: Add 4.8 g of Cu(NO3)2·3H2O and 2.6 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 35 mL of deionized water, place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min, set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt, with the Cu ion concentration being approximately 0.8 mol / L and the Zn ion concentration being approximately 0.34 mol / L; add 7.0 g of ethylenediamine as a dispersant to the mixed solution to prepare a precursor solution;

[0065] S2: Immerse 3 g of SPP molecular sieve (support 2) in 5 ml of the precursor solution, then dry it overnight in an oven at 110 °C, and then increase the temperature to 400 °C at a heating rate of 1 °C / min and hold it at 400 °C for 4 h.

[0066] S3 Repeat the operation of step S2 three times for the powder obtained in S2 to obtain the catalyst. The volume of the precursor solution impregnated each time is 4 mL; 3.8 mL; 3.6 mL.

[0067] Example 7: The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol in this example is carried out according to the following steps:

[0068] 1: Add 9.64 g of Cu(NO3)2·3H2O and 5.10 g of Zn(NO3)2·6H2O with a Cu / Zn ratio of 7 / 3 to 20 mL of deionized water, place it in a 360 W ultrasonic cleaner and ultrasonicate for 30 min, set the temperature to 40 °C to obtain a mixed aqueous solution of Cu salt and Zn salt, with the Cu ion concentration being approximately 1.6 mol / L and the Zn ion concentration being approximately 0.68 mol / L;

[0069] S2: Immerse 3 g of SPP molecular sieve (support 2) in 5 ml of the precursor solution, then dry it overnight in an oven at 110 °C, and then increase the temperature to 400 °C at a heating rate of 1 °C / min and hold it at 400 °C for 4 h.

[0070] The catalysts obtained in the above examples were characterized, see Figures 1-5 and Table 1 and Table 2:

[0071] Test conditions:

[0072] In the present invention, Figure 1 The XRD spectral data of the samples were detected using a Smartlab type powder X-ray diffractometer (XRD) from Rigaku Corporation, Japan. The step size was 0.02°, the scanning rate was 20° / min, the X-ray tube voltage was 40 kV, and the current was 150 mA.

[0073] Figure 2 The N2 gas adsorption and desorption tests were carried out using an IQ3 type physical adsorption instrument from Quantum Corporation, USA. First, the samples were degassed under vacuum at 300 °C for 10 hours. Subsequently, they were transferred to the analysis station for testing. The test gas was N2, the test temperature was 77 K, and the equilibrium time was 2 minutes.

[0074] Figure 3 The morphology of the examples was detected using a Gemini360 type scanning electron microscope (SEM) from ZESS Corporation, Germany.

[0075] Figure 4The morphology and metal particle size of the examples were detected using a J200 transmission electron microscope from JEOL, Japan.

[0076] Figure 5 A self-made chemisorption instrument with a TCD detector in the laboratory was used. The TCD temperature was 150 °C, the current was 150 mA, and the carrier gas was a 5% H2 / Ar mixture. First, the sample was pretreated in an Ar atmosphere at 350 °C for 2 h and then cooled to room temperature. Subsequently, a temperature-programmed test was carried out from room temperature to 800 °C at a heating rate of 10 °C / min.

[0077] Figure 1 XRD patterns of the SPP support and the catalysts prepared in Examples 1-7 are shown. The peaks at 2Theta = 7-9° and 21-26° are attributed to the characteristic peaks of the SPP molecular sieve. The characteristic peaks of SPP are included in all samples. No obvious characteristic diffraction peaks attributed to ZnO were observed in the XRD patterns of all examples, indicating that ZnO in the catalyst was highly dispersed. The peaks at 2Theta = 32.7, 35.6, 38.8, 48.9, and 61.5° are all peaks of CuO. Characteristic peaks of CuO exist in the XRD patterns of Examples 1, 2, 4, 5, and the comparative example. Obvious characteristic diffraction peaks of CuO were observed in Examples 1 and 2, indicating the presence of larger CuO particles; no characteristic diffraction peak of CuO was found in Example 3, indicating the absence of large CuO species and a high dispersion of CuO; a weak characteristic diffraction peak of CuO appeared in Example 4, indicating the beginning of a small amount of CuO aggregation; an obvious characteristic diffraction peak of CuO appeared in Example 5, indicating more CuO species aggregation. In Examples 1, 2, and 4, the same content of CuO was contained. The intensity of the CuO characteristic peak in the XRD pattern of Example 4 was lower, indicating that the size of CuO was smaller. It shows that after adding ethylenediamine as a dispersant, a better dispersion effect was achieved, which was due to the interaction between the precursor and the abundant Si-OH on the surface of the support. The results of Examples 3-5 showed that with the increase in the content of CuO, the CuO particles aggregated. No characteristic diffraction peak of CuO was also observed in Example 6, indicating a high dispersion of CuO particles in this sample. An obvious characteristic peak of CuO was observed in Example 7, and the peak height was significantly higher than that of the CuO peaks in Examples 1-6, indicating that the dispersion of CuO in this sample was significantly lower than that of the samples with the dispersant added. The XRD results showed that after adding the dispersant, the dispersion of CuO on the catalyst increased significantly, and ethylenediamine had the best dispersion effect as a dispersant.

[0078] Figure 2From the N2 adsorption - desorption curves of the SPP support (A) and Examples 1 - 7 (B), it can be seen that the adsorption - desorption curves of supports 1 and 2 are obvious type - I curves, and the desorption branch has an obvious desorption hysteresis loop, indicating that the supports have abundant mesopores. The micropore adsorption amounts of the supports are 0.075 and 0.062 cm 3 / g respectively, and the external specific surface areas are 474.5 and 524.8 m 2 / g respectively. The adsorption - desorption curves of Examples 1 - 7 are similar to those of the support. The adsorption amount, micropore volume and external specific surface area of the catalyst all show obvious decreases compared with SPP. The micropore volumes and external specific surface areas of Examples 1 - 6 are listed in Table 2. Among the examples with dispersants added, when ethylenediamine is used as the dispersant, the specific surface area and pore volume are the smallest, indicating that more highly dispersed CuO and ZnO enter the mesopores of the catalyst.

[0079] Figure 3 As can be seen from the scanning electron microscope images of the SPP support and Examples 1 - 7. Support 1 presents a self - assembled nanostructure of nanosheets ( Figure 3 A), with a spherical morphology, and the spherical size is about 100 nm. The morphologies of Examples 1 - 5 and Example 7 are also spherical ( Figure 3 B - F and I), with a spherical size of about 100 nm, which is consistent with SPP. Support 2 presents a self - assembled nanostructure of nanosheets ( Figure 3 G), with a spherical morphology, and the spherical size is about 400 nm; the morphology of Example 6 ( Figure 3 H) is also spherical, with a spherical size of about 400 nm, which is consistent with Support 2.

[0080] Figure 4From the TEM and STEM images of Examples 1-7, it can be seen that in Example 1, the CuO particle size distribution is relatively wide. That is, there are small particles with a size of 2-10 nm, and there are also CuO particles with a relatively large size (about 16 nm). The dispersion degree of Cu on this sample is 13.3%. In Example 2, the maximum particle size of CuO is 13 nm, and there are also small particles of 2-10 nm at the same time. The dispersion degree of Cu on this sample is 10.0%. In Example 3, the CuO particle size is about 2 nm, and the Cu dispersion degree is the highest (26.7%). In Example 4, the sample size is mainly distributed around 2-8 nm. The dispersion degree of Cu on this sample is 24%. In Example 5, the small particle size of the sample is distributed between 2-8 nm, and the size of some large particles exceeds 10 nm. The Cu dispersion degree on this sample is 7.9%. In Example 7, CuO particles with a size exceeding 20 nm can be clearly observed, indicating that the dispersion of CuO on this sample is poor. The results show that the CuO particles on the samples prepared after adding the dispersant can obtain a smaller size and a higher dispersion degree. All samples contain CuO particles of 2-8 nm. Among them, the dispersion degree of CuO is the best when ethylenediamine is used as the dispersant.

[0081] Figure 5 From the H2 temperature-programmed reduction curves of Examples 1-7, it can be seen that in all examples, CuO is reduced before 350 °C, and the position of the H2 consumption peak is before 280 °C, indicating that the CuO in Examples 1-5 has a high dispersion degree. There are two reduction peaks on the curve of Example 1, which are located at 190 and 270 °C respectively. There is a hydrogen consumption peak on the curve of Example 2 at 250 °C. There is a consumption peak at 240 °C in Example 3, which is the reduction peak of CuO with a high dispersion degree. The area of the H2 consumption peak of the samples in Examples 3-5 increases with the increase of the Cu content. At the same time, the position of the H2 consumption peak moves towards the high-temperature direction, indicating that the increase in the CuO particle size makes it more difficult to be reduced. There are mainly three H2 consumption peaks in Example 6. The reduction peaks of CuO are located at 190 and 270 °C, and the reduction peak at 340 °C is Cu + with a strong interaction with the carrier, indicating that the dispersion degree of CuO on the sample is very high.

[0082] Table 1 CuO particle size, CuO content, ZnO content and Cu dispersion degree of Examples 1-7.

[0083]

[0084] Table 2 Specific surface area and pore structure characteristics of the SPP carrier and Examples 1-7.

[0085]

[0086] Furthermore, the catalyst obtained by the above embodiments was used for catalytic experiments:

[0087] The reaction of hydrogenating carbon dioxide to methanol was carried out in a micro-pressure fixed-bed continuous flow reactor at a reaction temperature of 180 - 300 °C, GHSV = 3000 h -1 , V(H2):V(CO2) = 3:1, and the reaction pressure was 3 MPa; among them, the catalyst addition amount was 0.5 g, the raw material CO2 was 5 mL / min, and H2 was 15 mL / min (see Figure 6 and 7 , Table 3 - 7).

[0088] Table 3 CO2 conversion rate (%) of Examples 1 - 7.

[0089]

[0090]

[0091] Table 4 CO2 turnover frequency (h -1 ) of Examples 1 - 7.

[0092]

[0093] Table 5 Methanol space-time yield (g·h -1 ·g Cata -1 ) of Examples 1 - 7.

[0094]

[0095] Table 6 Methanol unit formation rate (g·h -1 ·g Cu -1 ) of Examples 1 - 7.

[0096]

[0097] From Figure 6 the CO2 conversion rate and CO2 turnover frequency of Examples 1 - 7, it can be seen that the CO2 conversion rate of Examples 1 - 7 increases with the increase of temperature and is close to the equilibrium conversion rate (Table 3). The only by-product of all examples participating in the reaction of hydrogenating CO2 to methanol is CO. The CO2 turnover frequencies of all examples exceed those of the CuZnAl catalyst prepared by the coprecipitation method (Table 4), indicating that CuO / ZnO increases the CO2 turnover frequency. Among them, the CO2 turnover frequency of Example 3 is the highest, which is 5 h at 260 °C -1 .

[0098] Figure 7From the methanol space-time yield and methanol unit formation rate of Examples 1-7, it can be seen that all samples have a high methanol space-time yield (Table 5) and methanol formation rate (Table 6), indicating that highly dispersed CuO / ZnO improves the reaction activity. With the increase of reaction temperature, both the methanol space-time yield and methanol formation rate first increase and then decrease, reaching the highest in the range of 220-260 °C. This is because the CO2 conversion rate increases with temperature, while the selectivity of methanol decreases with the increase of temperature (Table 7). The methanol unit formation rate of the catalyst after adding the dispersant increases significantly. Among them, the methanol unit formation rate of Example 3 is the highest, reaching 46.8 g·h -1 ·g Cu -1 .

[0099] The results of the activity test show that the CO2 conversion rate, TOF, methanol yield and formation rate of the samples after adding the dispersant have been significantly improved. Among them, the activity of hydrogenation of 2 to methanol on the sample with ethylenediamine as the precursor is the highest.

Claims

1. A catalyst for the hydrogenation of carbon dioxide to produce methanol, characterized in that, A spherical catalyst is obtained by uniformly dispersing CuO and ZnO as active components on a hierarchical pore self-supporting nanosheet zeolite molecular sieve support; wherein, CuO in the catalyst accounts for 8.3 - 34.7 wt.%, and ZnO accounts for 3.6 - 15.2 wt.%.

2. The catalyst according to claim 1, wherein The specific surface area of the catalyst is 90.0 - 433.3 m 2 / g, and the mesoporous specific surface area reaches 90.0 - 351.5 m 2 / g, with a mesoporous pore volume of 0.217 - 0.605 m 2 / g.

3. The catalyst according to claim 1 or 2, characterized in that, Active component particles with a size of 2 - 8 nm are uniformly dispersed and loaded on the surface of the catalyst support.

4. The catalyst according to claim 1 or 2, characterized in that, The support is a hierarchical pore self-supporting nanosheet zeolite molecular sieve (SPP molecular sieve), and the phase of the support is a five-membered ring chain zeolite molecular sieve, which is self-assembled by nanosheets in an intercalated manner; Among them, the specific surface area of the carrier is 581.1 - 630.2 m 2 / g.

5. A preparation method of the catalyst for hydrogenating carbon dioxide to prepare methanol according to claim 1, characterized in that S1 First, dissolve Cu salt and Zn salt in water, and then add an organic dispersant to prepare a precursor solution; S2 Immerse the support in the above precursor solution, and obtain the catalyst after drying and calcination.

6. The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol according to claim 5, characterized in that, The molar ratio of the Cu salt to the Zn salt is (6 - 8):

3.

7. The preparation method of the catalyst for hydrogenating carbon dioxide to produce methanol according to claim 5, characterized in that, The organic dispersant is one or several of ethylenediamine, citric acid or polyvinylpyrrolidone.

8. The method for preparing a catalyst for hydrogenating carbon dioxide to produce methanol according to claim 5 or 7, characterized in that, The addition amount of the dispersant is 0.21 - 1.03 times the mass of the metal salt.

9. An application of the catalyst according to claim 1 in catalyzing the hydrogenation of carbon dioxide to prepare methanol.

10. The application according to claim 9, wherein The reaction of hydrogenating carbon dioxide to prepare methanol is carried out in a micro-pressure fixed-bed continuous flow reactor. The reaction temperature is 180 - 300 °C, GHSV = 3000 h -1 , V(H2):V(CO2) = 3:1, and the reaction pressure is 3 MPa; among them, the addition amount of the catalyst is 0.5 g.

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